Physical vapor deposition (PVD) is commonly utilized for forming thin layers of material across a variety of substrates, including but not limited to, semiconductor substrates. FIG. 1 diagrammatically illustrates a PVD process. An exemplary PVD system 10 is shown having a substrate 12 positioned proximate a PVD target 14 (also referred to as a sputtering target). System 10 can utilize a monolithic target construction such as target 14 depicted, where monolithic indicates the target is machined or fabricated from a single piece of material and is used without combination with a target backing plate. Alternatively, a target construction can be a target assembly comprising a target and a backing plate (discussed further below). System 10 is not limited to a particular type of system or apparatus. Target 14 or an alternative target/backing plate assembly can have any of a number of configurations suitable for retaining the target within a desired sputtering apparatus.
Target 14 can comprise any suitable composition, and in the shown application comprises a conductive material. It is to be understood that the target can comprise any suitable construction for forming a desired film, and accordingly can also comprise non-conductive materials, such as for example, ceramic materials.
An exposed surface 16 of target 14 can be referred to as a sputtering surface. During a sputtering event, high energy particles generated by an RF plasma, for example, are impinged upon surface 16. The impingement causes displacement of material from target 14. The released material is diagrammatically illustrated by arrows 18. The released material forms a thin film 20 across an upper surface of substrate 12.
For purposes of the present description, the side of target 14 which includes sputtering surface 16 can be referred to as a front side of the target. Similarly, an opposing target surface 17 can be referred to as being on the back side of target 14.
During a sputtering process, substrate 12 is typically placed at a defined distance opposite surface 16 of target 14 which is mounted within a sputtering apparatus (not shown). When a target such as target 14, shown in FIG. 1, or alternatively a target/backing plate assembly is mounted within a PVD chamber, a portion of one or more surfaces of the target and/or backing plate can be in contact with interfacing surfaces of the PVD apparatus.
Referring to FIG. 2, a monolithic target is shown which has a sputtering surface 16 encircled by a mounting flange region 22. Target 14 is configured for mounting by providing mounting holes 24. Mounting holes 24 can in some instances be threaded for mounting using mounting bolts. Flange region 22 can comprise four holes as shown or can comprise any number of mounting holes as appropriate for the particular mounting configuration of the PVD system being utilized. Alternatively, target 14 can be mounted using a clamping or alternative configuration where holes 24 are not utilized and accordingly, flange region 22 can be configured to lack any holes (not shown).
Referring to FIG. 3, such shows a sectional side view of the target 14 taken along line 3-3 of FIG. 2. Mounting holes 24 can extend from a front side of target 28 through the flange region to backside 30. As discussed above, the number and placement of mounting poles 24 can vary depending upon the target mounting configuration of the system. Accordingly, the relative distance of placement of mounting holes 24 from target edge 32 can vary from that shown in FIG. 3.
As shown at each of FIGS. 2 and 3, target 14 has an inner radius R1 associated with the radius of the sputtering portion of the target, and an overall radius R2 which extends from a central axis designated ‘C’, to perimeter surface 32 and is inclusive of flange region 22 as well as the sputtering portion of the target. Target 14 can comprise an o-ring groove 26 (also referred to as a channel or gland) within flange region 22. In particular mounting configurations, o-ring channel 26 will be present as an opening in the front side of flange region 22. It is to be understood that the invention encompasses targets having alternative placement of o-ring channel 26, such as for example, at a distance from target edge 32 that differs from the placement shown in FIGS. 2 and 3.
Upon mounting within a sputtering apparatus, portions of flange region 22 can typically contact one or more interfacing surfaces of the deposition apparatus. Referring to FIG. 4, such shows an enlarged view of an exemplary flange region of a sputtering target. In a typical mounting configuration, at least a portion of the front surface of flange region 22 can interface a ceramic ring disposed between the target and the wall of the sputtering apparatus. An o-ring (not shown) is placed within o-ring channel 26 and upon mounting. Such o-ring contacts and preferably forms a seal between the flange region and the ceramic ring or other contacting surface.
Often, conventional targets show visible signs of rubbing of at least some of the surfaces on the front side of flange region 22 upon use of the target. Rubbing between the target surfaces can result in damage to the target and/or interfacing surfaces and can produce particles which can contaminate resulting films.
In conventional target design such as that exemplified in FIG. 4, an inner flange surface 36 extending from an inner groove corner 37 toward the sputtering region of the target is somewhat recessed relative to more outwardly disposed surfaces such as surface 40 which extends from an outer corner 38 of o-ring groove 26 toward mounting hole 24. It is noted that the amount of surface recess or offset between parallel surfaces 36 and 40 in a conventional target is not limited to a particular value and can be, for example, about 0.01 inches. In such target configurations, rubbing, scarring and/or scoring can occur primarily at corner 38 and/or across portions of surface 40.
Rubbing of the mounted target against the ceramic ring can be due to a number of factors. Upon impingement of high energy particles during a sputtering cycle, a portion of the energy of the particles is dissipated as thermal energy into the target material. Accordingly the temperature of target 14 increases during the sputtering process. Some PVD systems are configured to remove some of the thermal energy from the backside of the target or target/backing plate assembly utilizing a cooling circuit which typically comprises a water flow. As a result the entire target is at an elevated temperature during deposition with the target face being considerably hotter than the backside of the target. The temperature differential in the target leads to varied amounts of thermal expansion throughout the target and can result in motion. Such movement of the target can be enhanced in systems where pressurized water cooling is utilized on the backside and a vacuum is present at the opposing sputtering surface.
The mounting of the target and in certain instances the weight of the cooling fluid used in the cooling system can lead to severe o-ring deformation allowing increased contact between surfaces of the flange region and inner facing surfaces of the apparatus. The resulting rubbing can lead to contamination of the target by ceramic material and damage to the ceramic ring as well as the target. Contamination of the target can in turn lead to contamination of deposited layers thereby decreasing the quality of the layers. These negative effects can be intensified where larger targets or target assemblies are utilized.
In addition to the rubbing problems discussed above, target surface damage and/or contamination can occur due to arcing. Arcing can occur, for example, when gas or moisture becomes trapped within the o-ring groove during target mounting. Escape of such trapped gas or moisture during a deposition event can result in arcing resulting in damage to flange surfaces, target surfaces and/or ceramic ring surfaces which can in turn result in contamination of deposited layers. Another factor that may contribute to arching is the proximity of the groove vent relative to shielding present in the PVD chamber.
It is desirable to develop target constructions and methods for reducing target motion and rubbing that occurs in PVD processes.